Information recording medium and disk apparatus using the medium

ABSTRACT

According to one embodiment, an information recording medium has a plurality of recording layers, and records and reproduces information by using a semiconductor layer of 450 nm or less. When reproducing information, letting x be the frequency of repetitive recording of a shortest mark length and shortest space length of the information, the ratio of the value of a highest level to the value of a level at x/190 of a sum signal detected within the frequency range of x/3240 to x/190 is lower than 32 dB, or the ratio of the average value of the amplitudes of signals of repetitive recording of the shortest mark length and shortest space length to the value of the highest level within the frequency range of x/3240 to x/190 is higher than 10 dB.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 12/140,549 filed Jun. 17, 2008,and is based upon and claims the benefit of priority from JapanesePatent Application No. 2007-160307, filed Jun. 18, 2007, the entirecontents of which are incorporated herein by reference.

BACKGROUND

1. Field

One embodiment of the present invention relates to an informationrecording medium capable of recording and reproducing information byusing a short-wavelength laser beam such as a blue laser beam and, moreparticularly, to a write-once information recording medium, aninformation recording medium capable of recording information inmultiple layers, and a disk apparatus using the information recordingmedium.

2. Description of the Related Art

Optical disks are roughly classified into three types of disks, i.e., aROM disk for playback only, a write-once R disk, and a rewritable RW orRAM disk. As the volume of information increases, optical disks arebeing required to have large capacities and high transfer rates. To meetthe market demand for large capacities, a DVD-R disk having two recodinglayers instead of a normal single recording layer is being developed inorder to increase the capacity even when using a recording system usingthe same laser wavelength.

To further increase the capacity of an optical disk, an optical diskcalled an HD DVD has been developed. The data capacity of one side of anHD DVD-ROM or HD DVD-R is 15 GB that is three times or more the datacapacity of the conventional DVD, i.e., 4.7 GB. An organic dye materialis used in a recording layer of this HD DVD-R as described in, e.g.,Jpn. Pat. Appln. KOKAI Publication Nos. 2006-205683 and 2005-271587.

Unfortunately, forming two recording layers in this HD DVD-R is muchmore difficult than forming two recording layers in the DVD-R becausethe density is high. In particular, the deterioration of signalcharacteristics in the outer circumference is serious.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIG. 1 is a graph showing the relationship between the C/N of an L1layer at 5 to 85 kHz and the PRSNR of L1 when r=57 mm;

FIG. 2 is a view for explaining an example of the arrangement of anoptical disk according to an embodiment of the present invention;

FIG. 3 is a view showing examples of organic dye materials usable as anL-to-H organic dye layer;

FIGS. 4A to 4C are graphs each showing the relationship between thelaser beam wavelength and absorbance for a predetermined dye;

FIGS. 5A and 5B are graphs each showing the relationship between thelaser beam wavelength and absorbance for a predetermined dye;

FIG. 6 is a timing chart showing a method of recording rewritable dataon a write-once information storage medium according to the firstembodiment; and

FIG. 7 is a block diagram showing an outline of the arrangement of anoptical disk apparatus for playing back an optical disk.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings. In general,according to one embodiment of the invention, it is disclosed that aninformation recording medium having a plurality of recording layers andcapable of recording and reproducing information by emitting asemiconductor laser of 450 nm or less to the recording layer, and a diskapparatus using the information recording medium, wherein whenreproducing recorded information by detecting light reflected by therecording layer by using a light-detecting mechanism, letting x be thefrequency of repetitive recording of a shortest mark length and shortestspace length of the information, the ratio of the value of a highestlevel to the value of a level at x/190 of a sum signal detected by thelight-detecting mechanism is lower than 32 dB, or the ratio of theaverage value of the amplitudes of signals of repetitive recording ofthe shortest mark length and shortest space length to the value of thehighest level of the sum signal of the detected signals is higher than10 dB, within a frequency range represented by x/3240 to x/190.

In the present invention, recording and reproduction can be wellperformed from the inner circumference to the outer circumference of aninformation recording medium having multiple recording layers in whichrecording and reproduction are performed by using a wavelength of 450 nmor less.

The present inventors made extensive studies to solve the problem ofsignal characteristic deterioration in the prior art described above,and have found that low-frequency noise has a large influence on therecording characteristics particular in the outer circumference.

When a shortest mark length and shortest space length are 0.204 μm, forexample, the double of the shortest mark length is the length of onecycle of a repetitive recording pattern of the shortest mark andshortest space.

Length of one cycle=0.204 μm×2=0.408 μm

Also, when the rotational linear velocity of a disk is 6.61 m/s, a valueobtained by dividing the disk rotational linear velocity by the lengthof one cycle, i.e.,

6.61 (m/s)/0.408 μm=16.2M (l/s)=16.2 MHz

is the frequency of repetitive recording of the shortest mark andshortest space. When this frequency is substituted into x of

x/3240 to x/190

the frequency is 5 to 85 kHz. In this frequency band, the reflectedlight of a reproducing laser beam is measured using a spectrum analyzer.The spectrum analyzer was set such that the RBW (Resolution Band Width)was 1 kHz, and the VBW (Video Band Width) was 1 kHz, waveforms wereinput 64 times and averaged. The conditions were that a value at 85 kHzwas the noise level, a peak value between 5 kHz and 85 kHz was thecarrier level, and the C/N was (carrier level−noise level).

If the C/N value is higher than 32 dB, the recording/reproductioncharacteristics in the outer circumference often deteriorate.

An embodiment of the present invention can make the C/N lower than 32dB.

In another embodiment of the present invention, a carrier level Cst ofthe pattern of the shortest mark length and shortest space lengthindicates the average value of the amplitudes of reproduction signals ofrepetitive recording of the shortest mark length and shortest spacelength, and the Cst/C is the ratio of the Cst to a peak value C between5 kHz and 85 kHz. The other embodiment can make the Cst/C higher than 10dB. If the Cst/C is equal to or lower than 10 dB, the error ratecharacteristic of a recording signal often deteriorates.

Still another embodiment of the present invention has the advantage thatgood recording/reproduction characteristics can be obtained from theinner circumference to the outer circumference of the informationrecording medium by making the C/N lower than 32 dB and the Cst/C higherthan 10 dB.

Note that the C/N can be 0 (inclusive) to 32 (exclusive) dB from thepractical viewpoint.

Note also that the Cst/C can be 10 (exclusive) to 60 (inclusive) dB fromthe practical viewpoint.

If the Cst/C is higher than 60 dB, the circuits of the apparatussaturate because the signal is too large. This often makes it impossibleto correctly reproduce the signal.

FIG. 1 shows the relationship between the C/N of an L1 recording layerat 5 to 85 kHz and the PRSNR when r=57 mm of the information recordingmedium according to the present invention.

The PRSNR stands for Partial Response Signal to Noise Ratio. The higherthe value, the better the signal characteristics. In this embodiment,the drive can read data when the PRSNR is 12 or more. The PRSNR ispreferably 15 or more.

The L1 recording layer is the second recording layer from the laser beamincident side.

FIG. 2 is a view for explaining an example of the arrangement of awrite-once, single-sided, double-layered optical disk 100 as an exampleof the optical disk according to an embodiment of the present invention.As indicated by (a) and (b) in FIG. 2, the optical disk 100 has adisk-like transparent resin substrate 101 made of a synthetic resinmaterial such as polycarbonate (PC). The transparent resin substrate 101has concentric grooves or a spiral groove. The transparent resinsubstrate 101 can be manufactured by injection molding by using astamper.

An organic dye recording layer 105 as a first layer (L0) and asemi-light-transmitting reflecting layer 106 are sequentially stacked onthe 0.59-mm thick transparent resin substrate 101 made of polycarbonateor the like, and a photopolymer (2P resin) 104 is formed on thesemi-light-transmitting reflecting layer 106 by spin coating. The grooveshape of a second layer (L1) is transferred onto the photopolymer 104,and an organic dye recording layer 107 as the second layer and areflecting film 108 made of, e.g., silver or a silver alloy aresequentially stacked. A 0.59-mm thick transparent resin substrate (ordummy substrate) 102 is laminated on the substrate on which the L0 andL1 recording layers are stacked, with an UV-curing resin (adhesivelayer) 103 interposed between the two substrates. The organic dyerecording layers 105 and 107 form a two-layered structure in which thesemi-transmitting reflecting layer 106 and interlayer 104 aresandwiched. The total thickness of the laminated optical disk thusobtained is about 1.2 mm.

A spiral groove having, e.g., a track pitch of 0.4 μm and a depth of 60nm is formed (in each of the L0 and L1 layers) on the transparent resinsubstrate 101 or photopolymer 104. This groove wobbles, and addressinformation is recorded on the wobble. The recording layers 105 and 107containing an organic dye are formed on the transparent resin substrate101 or photopolymer 104 so as to fill the groove.

As the organic dye forming the recording layers 105 and 107, it ispossible to use an organic dye having a maximum absorption wavelengthregion shifted to wavelengths longer than the recording wavelength(e.g., 405 nm). Also, the organic dye is designed so as not toextinguish absorption in the recording wavelength region but to have aconsiderable light absorption in the long-wavelength region (e.g., 450to 600 nm).

When dissolved in a solvent, the above-mentioned organic dye (practicalexamples will be described later) can be easily applied in the form of aliquid onto the surface of the transparent resin substrate by spincoating. In this case, the film thickness can be accurately controlledby controlling the ratio of dilution by the solvent and the rotationalspeed of spin coating.

Note that the light reflectance is low when focusing or tracking isperformed on tracks by a recording laser beam before information isrecorded. After that, the light reflectance of a recording mark portionrises because the laser beam causes a decomposition reaction of the dyeand the light absorbance decreases. This achieves a so-called,Low-to-High (or L-to-H) characteristic by which the light reflectance ofa recording mark portion formed by emitting the laser beam is higherthan that before the laser beam is emitted.

In the embodiment of the present invention, an example of a physicalformat applied to the L0 and L1 layers existing on the transparent resinsubstrate 101 and photopolymer (2P resin) 104 is as follows. That is,general parameters of the write-once, single-sided, double-layered diskare almost the same as those of a single-layered disk, except that therecording capacity usable by a user is 30 GB, the inner diameter of adata area is 24.6 mm in layer 0 (the L0 layer) and 24.7 mm in layer 1(the L1 layer), and the outer diameter of the data area is 58.1 mm (inboth layers 0 and 1).

In the optical disk 100 indicated by (a) in FIG. 2, a system lead-inarea SLA includes a control data section as indicated by (c) in FIG. 2.This control data section includes parameters concerning recording, suchas the recording power (peak power) and bias power, as a part ofphysical format information and the like, for each of L0 and L1.

Also, as indicated by (d) in FIG. 2, mark/space recording is performedon tracks in a data area DA of the optical disk 100 by a laser having apredetermined recording power (peak power) and bias power. As indicatedby (e) in FIG. 2, this mark/space recording records object data (e.g.,VOB) of a high-resolution TV broadcasting problem or the like andmanagement information (VMG) of the object data on the tracks (of L0and/or L1) in the data area DA.

As the Low-to-High (or L-to-H) organic dye usable in the embodiment ofthe present invention, it is possible to use an organic dye including adye portion and counterion (anion) portion, or an organic metal complex.As the dye portion, it is possible to use, e.g., a cyanine dye, styryldye, porphyrin dye, or azo dye. A cyanine dye, styryl dye, and azo dyeare particularly suitable because the absorptance to the recordingwavelength is readily controllable.

When the transparent resin substrate is coated with a thin recordingfilm containing a monomethine cyanine dye having a monomethine chainamong other L-to-H organic dyes, the maximum absorption and theabsorbance in the recording wavelength region (400 to 405 nm) can beeasily adjusted to nearly 0.3 to 0.5, preferably, nearly 0.4. This makesit possible to improve the recording/reproduction characteristics, andwell design both the light reflectance and recording sensitivity.

The anion portion of the organic dye is preferably an organic metalcomplex from the viewpoint of the optical stability as well. An organicmetal complex containing cobalt or nickel as its central metalparticularly has a high optical stability.

An azo metal complex or the like can be used as the organic metalcomplex. The azo metal complex has a high solubility when2,2,3,3-tetrafluoro-1-propanol (TFP) is used as a solvent. Thisfacilitates the preparation of a solution for spin coating. In addition,since the solution can be recycled after spin coating, the manufacturingcost of the information recording medium can be reduced.

Note that the organic metal complex can be dissolved in a TFP solutionand applied by spin coating. When used in an information recordingmedium having two recording layers, the azo metal complex isparticularly favorable as the L0 recording layer made of a thin Ag alloylayer because the azo metal complex hardly deforms after recording.Although Cu, Ni, Co, Zn, Fe, Al, Ti, V, Cr, or Y can be used as thecentral metal, Cu, Ni, and Co especially have a high reproducing lightresistance. Cu has no genetic toxicity and improves the quality of arecording/reproduction signal.

Various materials can be used as ligands surrounding the central metal.Examples are dyes represented by formulas (D1) to (D6) below. It is alsopossible to form another structure by combining these ligands.

FIG. 3 shows four examples of dyes A to D as organic dye materialsusable as the L-to-H organic dye layer usable in the present invention.The dye A has a styryl dye as a dye portion (cation portion) and azometal complex 1 as an anion portion. The dye C has a styryl dye as a dyeportion (cation portion) and azo metal complex 2 as an anion portion.The dye D has a monomethinecyanine dye as a dye portion (cation portion)and azo metal complex 1 as an anion portion. Note that an organic metalcomplex can also be used singly. As an example, the dye B is a nickelcomplex dye.

Formula (E1) below indicates the formula of the styryl dye as the dyeportions of the dyes A and C. Formula (E2) below indicates the formulaof the azo metal complex as the anion portions of the dyes A and C.Formula (E3) below indicates the formula of the monomethinecyanine dyeas the dye portion of the dye D. Formula (E4) below indicates theformula of the azo metal complex as the anion portion of the dye D.

In the formula of the styryl dye, Z₃ represents an aromatic ring, andthis aromatic ring may have a substituent group. Y₃₁ represents a carbonatom or hetero atom. R₃₁, R₃₂, and R₃₃ represent the same aliphatichydrocarbon group or different aliphatic hydrocarbon groups, and thesealiphatic hydrocarbon groups may have a substituent group. R₃₄ and R₃₅each independently represent a hydrogen atom or appropriate substituentgroup. When Y₃₁ is a hetero atom, one or both of R₃₄ and R₃₅ do notexist.

In the formula of the monomethinecyanine dye, Z₁ and Z₂ represent thesame aromatic ring or different aromatic rings, and these aromatic ringsmay have a substituent group. Y₁₁ and Y₁₂ each independently represent acarbon atom or hetero atom. R₁₁ and R₁₂ represent aliphatic hydrocarbongroups, and these aliphatic hydrocarbon groups may have a substituentgroup. R₁₃, R₁₄, R₁₅, and R₁₆ each independently represent a hydrogenatom or appropriate substituent group. When Y₁₁ and Y₁₂ are heteroatoms, some or all of R₁₃, R₁₄, R₁₅, and R₁₆ do not exist.

Examples of the monomethinecyanine dye used in this embodiment are dyesobtained by bonding identical or different cyclic nuclei which may haveone or a plurality of substituent groups to the two ends of amonomethine chain which may have one or a plurality of substituentgroups. Examples of the cyclic nuclei are an imidazoline ring, imidazolering, benzoimidazole ring, α-naphthoimidazole ring, β-naphthoimidazolering, indole ring, isoindole ring, indolenine ring, isoindolenine ring,benzoindolenine ring, pyridinoindolenine ring, oxazoline ring, oxazolering, isoxazole ring, benzoxazole ring, pyridinoxazole ring,α-naphthoxazole ring, β-naphthoxazole ring, selenazoline ring,selenazole ring, benzoselenazole ring, α-naphthoselenazole ring,β-naphthoselenazole ring, thiazoline ring, thiazole ring, isothiazolering, benzothiazole ring, α-naphthothiazole ring, β-naphthothiazolering, tellurazoline ring, tellurazole ring, benzotellurazole ring,α-naphthotellurazole ring, β-naphthotellurazole ring, acridine ring,anthracene ring, isoquinoline ring, isopyrrole ring, imidanoxaline ring,indandione ring, indazole ring, indaline ring, oxadiazole ring,carbazole ring, xanthene ring, quinazoline ring, quinoxaline ring,quinoline ring, chroman ring, cyclohexanedione ring, cyclopentanedionering, cinnoline ring, thiodiazole ring, thioxazolidone ring, thiophenering, thionaphthene ring, thiobarbituric acid ring, thiohydantoin ring,tetrazole ring, triazine ring, naphthalene ring, naphthyridine ring,piperazine ring, pyrazine ring, pyrazole ring, pyrazoline ring,pyrazolidine ring, pyrazolone ring, pyran ring, pyridine ring,pyridazine ring, pyrimidine ring, pyrylium ring, pyrrolidine ring,pyrroline ring, pyrrole ring, phenazine ring, phenanthrizine ring,phenanthrene ring, phenanthroline ring, phtharazine ring, puterizinering, furazane ring, furan ring, purine ring, benzene ring, benzoxazinering, benzopyran ring, morpholine ring, and rhodanine ring.

In the formulas of the monomethinecyanine dye and styryl dye, Z₁ to Z₃represent aromatic rings such as a benzene ring, naphthalene ring,pyridine ring, quinoline ring, and quinoxaline ring, and these aromaticrings may have one or a plurality of substituent groups. Examples of thesubstituent groups are aliphatic hydrocarbon groups such as a methylgroup, trifluoromethyl group, ethyl group, propyl group, isopropylgroup, butyl group, isobutyl group, sec-butyl group, tert-butyl group,pentyl group, isopentyl group, neopentyl group, tert-pentyl group,1-methylpentyl group, 2-methylpentyl group, hexyl group, isohexyl group,5-methylhexyl group, heptyl group, and octyl group; alicyclichydrocarbon groups such as a cyclopropyl group, cyclobutyl group,cyclopentyl group, and cyclohexyl group; aromatic hydrocarbon groupssuch as a phenyl group, biphenylyl group, o-tolyl group, m-tolyl group,p-tolyl group, xylyl group, mesityl group, o-cumenyl group, m-cumenylgroup, and p-cumenyl group; ether groups such as a methoxy group,trifluoromethoxy group, ethoxy group, propoxy group, isopropoxy group,butoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group,phenoxy group, and benzoyloxy group; ester groups such as amethoxycarbonyl group, trifluoromethoxycarbonyl group, ethoxycarbonylgroup, propoxycarbonyl group, acetoxy group, and benzoyloxy group;halogen groups such as a fluoro group, chloro group, bromo group, andiodo group; thio groups such as a methylthio group, ethylthio group,propylthio group, butylthio group, and phenylthio group; sulfamoylgroups such as a methylsulfamoyl group, dimethylsulfamoyl group,ethylsulfamoyl group, diethylsulfamoyl group, propylsulfamoyl group,dipropylsulfamoyl group, butylsulfamoyl group, and dibutylsulfamoylgroup; amino groups such as a primary amino group, methylamino group,dimethylamino group, ethylamino group, diethylamino group, propylaminogroup, dipropylamino group, isopropylamino group, diisopropylaminogroup, butylamino group, dibutylamino group, and piperidino group;carbamoyl groups such as a methylcarbamoyl group, dimethylcarbamoylgroup, ethylcarbamoyl group, diethylcarbamoyl group, propylcarbamoylgroup, and dipropylcarbamoyl group; and a hydroxy group, carboxy group,cyano group, nitro group, sulfino group, sulfo group, and mesyl group.Note that in these formulas, Z₁ and Z₂ can be the same or different.

In the formulas of the monomethinecyanine dye and styryl dye, Y₁₁, Y₁₂,and Y₃₁ each represent a carbon atom or hetero atom. Examples of thehetero atom are group-XV and group-XVI atoms in the periodic table, suchas a nitrogen atom, oxygen atom, sulfur atom, selenium atom, andtellurium atom. Note that the carbon atom represented by Y₁₁, Y₁₂, orY₃₁ may also be an atomic group mainly containing two carbon atoms, suchas an ethylene group or vinylene group. Note also that Y₁₁ and Y₁₂ inthe formula of the monomethinecyanine dye can be the same or different.

In the formulas of the monomethinecyanine dye and styryl dye, R₁₁, R₁₂,R₁₃, R₃₂, and R₃₃ each represent an aliphatic hydrocarbon group.Examples of the aliphatic hydrocarbon group are a methyl group, ethylgroup, propyl group, isopropyl group, isopropenyl group, 1-propenylgroup, 2-propenyl group, butyl group, isobutyl group, sec-butyl group,tert-butyl group, 2-butenyl group, 1,3-butadienyl group, pentyl group,isopentyl group, neopentyl group, tert-pentyl group, 1-methylpentylgroup, 2-methylpentyl group, 2-pentenyl group, hexyl group, isohexylgroup, 5-methylhexyl group, heptyl group, and octyl group. Thisaliphatic hydrocarbon group may have one or a plurality of substituentgroups similar to those of Z₁ to Z₃.

Note that R₁₁ and R₁₂ in the formula of the monomethinecyanine dye canbe the same or different, and R₁₃, R₃₂, and R₃₃ in the formula of thestyryl dye can be the same or different.

R₁₃ to R₁₆, R₃₄, and R₃₅ in the formulas of the monomethinecyanine dyeand styryl dye each independently represent a hydrogen atom orappropriate substituent group in the individual formulas. Examples ofthe substituent group are aliphatic hydrocarbon groups such as a methylgroup, trifluoromethyl group, ethyl group, propyl group, isopropylgroup, butyl group, isobutyl group, sec-butyl group, tert-butyl group,pentyl group, isopentyl group, neopentyl group, tert-pentyl group,1-methylpentyl group, 2-methylpentyl group, hexyl group, isohexyl group,5-methylhexyl group, heptyl group, and octyl group; ether groups such asa methoxy group, trifluoromethoxy group, ethoxy group, propoxy group,butoxy group, tert-butoxy group, pentyloxy group, phenoxy group, andbenzoyloxy group; halogen groups such as a fluoro group, chloro group,bromo group, and iodo group; and a hydroxy group, carboxy group, cyanogroup, and nitro group. Note that when Y₁₁, Y₁₂, and Y₃₁ are heteroatoms in the formulas of the monomethinecyanine dye and styryl dye, someor all of R₁₃ to R₁₆ in Z₁ and Z₂ and one or both of R₃₄ and R₃₅ in Z₃do not exist.

In the formula of the azo metal complex, A and A′ represent 5- to10-membered heterocyclic groups which are the same or different and eachcontain one or a plurality of hetero atoms selected from a nitrogenatom, oxygen atom, sulfur atom, selenium atom, and tellurium atom.Examples of the heterocyclic groups are a furyl group, thienyl group,pyrrolyl group, pyridyl group, piperidino group, piperidyl group,quinolyl group, and isoxazolyl group. This heterocyclic group may haveone or a plurality of substituent groups. Examples of the substituentgroups are aliphatic hydrocarbon groups such as a methyl group,trifluoromethyl group, ethyl group, propyl group, isopropyl group, butylgroup, isobutyl group, sec-butyl group, tert-butyl group, pentyl group,isopentyl group, neopentyl group, tert-pentyl group, 1-methylpentylgroup, 2-methylpentyl group, hexyl group, isohexyl group, and5-methylhexyl group; ester groups such as a methoxycarbonyl group,trifluoromethoxycarbonyl group, ethoxycarbonyl group, propoxycarbonylgroup, acetoxy group, trifluoroacetoxy group, and benzoyloxy group;aromatic hydrocarbon groups such as a phenyl group, biphenylyl group,o-tolyl group, m-tolyl group, p-tolyl group, o-cumenyl group, m-cumenylgroup, p-cumenyl group, xylyl group, mesityl group, styryl group,cinnamoyl group, and naphthyl group; and a carboxy group, hydroxy group,cyano group, and nitro group.

Note that an azo compound forming the azo-based organic metal complexrepresented by the formula can be obtained in accordance with theconventional method by reacting diazonium salt having R₂₁ and R₂₂ or R₂₃and R₂₄ corresponding to the formula with a heterocyclic compound havingan active methylene group adjacent to a carbonyl group in a molecule.Examples of the heterocyclic compound are an isoxazolone compound,oxazolone compound, thionaphthene compound, pyrazolone compound,barbituric acid compound, hydantoin compound, and rhodanine compound.Y₂₁ and Y₂₂ represent hetero atoms which are the same or different andselected from group-XVI elements in the periodic table, e.g., an oxygenatom, sulfur atom, selenium atom, and tellurium atom.

The azo metal complex represented by the formula is normally used in theform of a metal complex in which one or a plurality of azo metalcomplexes are coordinated around a metal (central atom). Examples of ametal element serving as the central atom are scandium, yttrium,titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium,osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper,silver, gold, zinc, cadmium, and mercury, and cobalt is particularlyfavorable.

FIG. 4A shows the change in absorbance of the dye A to the wavelength ofan emitted laser beam. FIG. 4B shows the change in absorbance of the dyeB to the wavelength of an emitted laser beam. FIG. 4C shows the changein absorbance of the dye C to the wavelength of an emitted laser beam.

FIG. 5A shows the change in absorbance of the dye D to the wavelength ofan emitted laser beam. FIG. 5B shows the change in absorbance of theanion portion of the dye D to the wavelength of an emitted laser beam.

As is evident from the characteristics shown in FIGS. 4A to 5B, the dyesA to D each have a maximum absorption wavelength region shifted towavelengths longer than the recording wavelength (405 nm). Thewrite-once optical disk explained in this embodiment comprises therecording film containing the organic dye having the characteristics asdescribed above, and is given the so-called L-to-H characteristic bywhich the light reflectance after laser beam emission is higher thanthat before laser beam emission. Even when a short-wavelength laser beamsuch as a blue laser beam is used, therefore, this write-once opticaldisk is superior in, e.g., storage durability, reproduction signal S/Nratio, and bit error rate, and capable of recording and reproducinginformation at a high density with performance on a well practicallevel.

That is, in this write-once optical disk, the maximum absorptionwavelength of the recording film containing the organic dye is longerthan the wavelength of the recording laser beam. Since this makes itpossible to reduce the absorption of short-wavelength light such asultraviolet radiation, the optical stability and the reliability ofinformation recording/reproduction improve.

Also, since the light reflectance is low when information is recorded,no cross write occurs owing to reflective diffusion. Therefore, evenwhen information is recorded on an adjacent track, it is possible toreduce the deterioration of the reproduction signal S/N ratio and biterror rate. Furthermore, the contrast and resolution of a recording markcan be kept high even against heat. This facilitates recordingsensitivity design.

When a dye having a maximum absorption wavelength region shifted towavelengths shorter than the recording wavelength (405 nm) is used asthe recording film, the write-once optical disk explained in thisembodiment is given a so-called H-to-L characteristic by which the lightreflectance after laser beam emission is lower than that before laserbeam emission. Even when a short-wavelength laser beam such as a bluelaser beam is used, therefore, this write-once optical disk has a highreflectance, is superior in, e.g., reproduction signal S/N ratio and biterror rate, and is capable of recording and reproducing information at ahigh density with performance on a well practical level.

That is, in this write-once optical disk, the maximum absorptionwavelength of the recording film containing the organic dye is shorterthan the wavelength of the recording laser beam. Since this makes itpossible to absorb or more or less reflect short-wavelength light suchas ultraviolet radiation, the optical stability and the reliability ofinformation recording/reproduction improve.

Furthermore, the contrast and resolution of a recording mark can be kepthigh even against heat. This facilitates recording sensitivity design.

Example

A transparent resin substrate 120 mm in diameter and 0.6 mm in thicknesshaving concentric grooves and lands or a spiral groove and land on thesurface and made of, e.g., polycarbonate was prepared.

A 1.2-wt % 2,2,3,3-tetrafluoro-1-propanol (TFP) solution of an organicdye represented by formula (D1) described previously was prepared.

Subsequently, an organic dye layer was formed on the transparent resinsubstrate by coating it with the TFP solution by spin coating. Thethickness from the groove bottom of the organic dye layer after coatingwas 60 nm. A 100-nm thick light-reflecting layer made of an Ag alloy wasstacked on the obtained organic dye layer by sputtering, therebyobtaining a recording layer in which the organic dye layer andlight-reflecting layer were stacked.

In addition, the light-reflecting layer was coated with a UV-curingresin by spin coating, and a transparent resin substrate 102 having athickness of 0.60 mm was laminated on the UV-curing resin, therebyobtaining a single-sided, double-layered, write-once informationrecording medium.

The dye represented by formula (D1) was an organic metal complex.

Using the information storage medium (a single-sided dual-layerevaluation disc) produced as described above, an experiment forevaluating a reproduction signal is performed.

The apparatus used for evaluation is optical disc evaluation apparatusODU-1000 manufactured by Pulstec Industrial Co., Ltd. This apparatus hasa laser wavelength of 405 nm and NA of 0.65. The linear velocity inrecording and reproduction is selected to be 6.61 m/s. A recordingsignal is 8-12 modulated random data, and information is recorded byusing a laser waveform containing a given recording power and two biaspowers 1 and 2 as shown in FIG. 6. The recording conditions applied tothe evaluation are as follows.

Explanation on Recording Conditions

(Information of Write Strategy)

Referring to FIG. 6, a description will be given with respect to arecording waveform (exposure condition at the time of recording) usedwhen the optimal recording power is checked. The exposure levels at thetime of recording have four levels of recording power (peak power), biaspower 1, bias power 2, and bias power 3. When long (4T or more)recording mark 9 is formed, modulation is carried out in the form ofmulti-pulses between recording power (peak power) and bias power 3. Inthe embodiment, in any of the H format and B format systems, a minimummark length relevant to channel bit length T is obtained as 2T. In thecase where the minimum mark of 2T is recorded, one write pulse of therecording power (peak power) level after bias power 1 is used as shownin FIG. 6, and bias power 2 is temporarily obtained immediately afterthe write pulse. In the case where 3T recording mark 9 is recorded, biaspower 2 is temporarily used after exposing two write pulses, a firstpulse and a last pulse of recording power (peak power) level thatfollows bias power 1. In the case where recording mark 9 having a lengthof 4T or more is recorded, bias power 2 is used after the exposure ismade with multi-pulse and write pulse.

The vertical dashed line in FIG. 6 shows a channel clock cycle. When a2T minimum mark is recorded, the laser power is raised at a positiondelayed by TSFP from the clock edge, and fallen at a position delayed byTELP from the one-clock passing portion. The just-subsequent cycleduring which the laser power is set at bias power 2 is defined as TLC.Values of TSFP, TELP, and TLC are recorded in physical formatinformation PFI contained in control data zone CDZ in the case of the Hformat.

In the case where a 3T or more long recording mark is formed, the laserpower is risen at a position delayed by TSFP from the clock edge, andlastly, ended with a last pulse. Immediately after the last pulse, thelaser power is kept at bias power 2 during the period of TLC. Shifttimes from the clock edge to the rise/fall timing of the last pulse aredefined as TSLP, TELP. In addition, a shift time from the clock edge tothe fall timing of the last pulse is defined as TEFP, and further, aninterval of a single pulse of the multi-pulse is defined as TMP.

Each of intervals TELP-TSFP, TMP, TELP-TSLP, and TLC is defined as ahalf-value wide relevant to the maximum value. In addition, in theembodiment, the above parameter setting ranges are defined as follows:

0.25T≦TSFP≦1.50T  (eq. 01)

0.00T≦TELP≦1.00T  (eq. 02)

1.00T≦TEFP≦1.75T  (eq. 03)

−0.10T≦TSLP≦1.00T  (eq. 04)

0.00T≦TLC≦1.00T  (eq. 05)

0.15T≦TMP≦0.75T  (eq. 06)

Further, in the embodiment, the values of the above described parameterscan be changed or modified according to the recording mark length (MarkLength) and the immediately preceding/immediately succeeding spacelength (Leading/Trailing space length).

In this embodiment, the shortest mark length is 0.204 μm, and the diskrotational linear velocity is 6.61 m/s. Therefore, the frequency of therepetitive pattern of the shortest mark and shortest space is 16.2 MHz.When this frequency is substituted into x of

x/3240 to x/190

the range to be measured by a spectrum analyzer is 5 to 85 kHz. Withinthis range, the N level was −89.8 dBrm at 85 kHz, and the highest level(C level) was −66.7 dBm. From the results, the C/N was 23.1 dB (=valueof C level−value of N level). When information was recorded, the PRSNRwas 18.7 in the inner circumference of L0, 17.6 in the outercircumference of L0, 23.1 in the inner circumference of L1, and 17.0 inthe outer circumference of L1. That is, it was possible to obtainfavorable recording characteristics from the inner circumference to theouter circumference. When 2T as the shortest mark was repetitivelyrecorded with this optimum recording power (the recording power by whichthe highest SbER and PRSNR were obtained), the carrier level (Cst)measured by the spectrum analyzer was −43.5 dB. The Cst/C was 23.2 dB.

The carrier level (Cst) indicates the average value of the amplitudes ofreproduction signals obtained when 2T was repetitively recorded with theoptimum recording power and then reproduced.

Comparative Example

An information recording medium was manufactured following the sameprocedures as in the example, and information was recorded. Within therange of 5 to 85 kHz, the N level was −89.0 dBm at 85 kHz, and the Clevel was −49.7 dBm. From the results, the C/N was 39.3 dB. Wheninformation was recorded, the PRSNR was 20.9 in the inner circumferenceof L0, 19.8 in the outer circumference of L0, 21.2 in the innercircumference of L1, and 11.4 in the outer circumference of L1. That is,it was possible to obtain favorable recording characteristics in theinner circumferences of L0 and L1, but the characteristics deterioratedin the outer circumferences. When 2T as the shortest mark wasrepetitively recorded with this optimum recording power (the recordingpower by which the highest SbER and PRSNR were obtained), the Cstmeasured by a spectrum analyzer was −45.0 dB. The Cst/C was 4.7 dB.

In this comparative example, the characteristics deteriorated in theouter circumferences although the information recording medium wasmanufactured following the same procedures as in the above embodiment.This is so because the signal characteristics deteriorate in the outercircumferences owing to a high density resulting from two layers.

The present invention can simply evaluate a medium in which thecharacteristics deteriorate by the method as described above, and canselect only a medium by which good signal characteristics can beobtained from the inner circumference to the outer circumference.

Note that the present invention is not limited to the above example and,when carried out at present or in the future, can be variously modifiedwithout departing from the spirit and scope of the invention on thebasis of techniques usable at that time. For example, the presentinvention can also be carried out not only on a double-layered disk butalso on an optical disk having three or more recording layers that willbe put into practical use in the future.

An optical disk apparatus for reproducing information recorded on theabove-mentioned optical disk will be explained below.

FIG. 7 is a block diagram showing an outline of the arrangement of theoptical disk apparatus for playing back an optical disk.

As shown in FIG. 7, an optical disk is, e.g., the single-sided,double-layered optical disk shown in FIG. 2. A short-wavelengthsemiconductor laser source 120 is used as the light source. Thewavelength of the exit beam is in, e.g., a violet wavelength band of 400to 410 nm. An exit beam 110 from the semiconductor laser source 120 iscollimated into a parallel beam by a collimating lens 121, and enters anobjective lens 124 through a polarizing beam splitter 122 and λ/4 plate123. After that, the beam 110 is focused on each information recordinglayer through the substrate of the optical disk D. Reflected light 111from the information recording layer of the optical disk D istransmitted through the substrate of the optical disk D again, andreflected by the polarizing beam splitter 122 through the objective lens124 and λ/4 plate 123. After that, the reflected light 111 enters alight-detecting mechanism through a condenser lens 125.

The light-detecting mechanism includes a photodetector 127 and an I/Vamplifier (current-to-voltage converter) that is not shown. Alight-receiving portion of the photodetector 127 is normally dividedinto a plurality of portions, and each light-receiving portion outputsan electric current corresponding to the light intensity. The I/Vamplifier (current-to-voltage converter) converts the output electriccurrent into a voltage, and applies the voltage to an arithmetic circuit140. The arithmetic circuit 140 calculates, e.g., a tilt error signal,HF signal, focusing error signal, and tracking error signal from theinput voltage signal. The tilt error signal is used to perform tiltcontrol. The HF signal is used to reproduce information recorded on theoptical disk D. A sum signal used in the present invention is this HFsignal. The focusing error signal is used to perform focusing control.The tracking error signal is used to perform tracking control.

An actuator 128 can drive the objective lens 124 in the verticaldirection, disk radial direction, and tilt direction (the radialdirection or/and tangential direction). A servo driver 150 controls theactuator 128 so that the objective lens 124 follows information trackson the optical disk D. Note that there are two different tiltdirections. One is “a radial tilt” that occurs when the disk surfaceinclines toward the center of an optical disk. The other is “atangential tilt” that occurs in the tangential direction of a track. Atilt that generally occurs owing to the warpage of a disk is the radialtilt. It is necessary to take account of not only a tilt that occursduring the manufacture of a disk but also a tilt that occurs owing to achange with time or a rapid change in use environment. The optical diskof the present invention can be played back by using the optical diskapparatus like this.

Also, the individual embodiments may also be appropriately combined asmuch as possible when practiced. In this case, the combined effects canbe obtained. Furthermore, these embodiments include inventions invarious stages, so various inventions can be extracted by properlycombining a plurality of disclosed constituent elements. For example,even when some of all the constituent elements disclosed in theembodiments are deleted, an arrangement from which these constituentelements are deleted can be extracted as an invention.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

1. An optical recording medium comprising a plurality of recordinglayers configured to record or reproduce information using light with apredetermined wavelength, wherein a period of channel clocks used torecord at least one recording mark on the recording layer is assumed tobe T, the information is recordable on the recording mark with a lengthof 2T, 3T, or more, multi-pulses are used to record the recording markwith the length of 3T or more, the multi-pulses including a last pulseat an end thereof, and the recording mark with the length of 3T or moreis recorded with a condition that a width of the last pulse falls withina range from 0T to 1.10T.
 2. A method of recording information on anoptical recording medium comprising a plurality of recording layersconfigured to record or reproduce the information using light with apredetermined wavelength, wherein a period of channel clocks used torecord at least one recording mark on the recording layer is assumed tobe T, the information is recordable on the recording mark with a lengthof 2T, 3T, or more, multi-pulses are used to record the recording markwith the length of 3T or more, the multi-pulses includes a last pulse atan end thereof, and the recording mark with the length of 3T or more isrecorded provided that a width of the last pulse falls within a rangefrom 0T to 1.10, the method comprising: the information is recorded onat least one of the recording layers using the light.
 3. A method ofreproducing information from an optical recording medium comprising aplurality of recording layers on which the information is at leastpartly recorded using light with a predetermined wavelength, wherein aperiod of channel clocks used to record at least one recording mark onthe recording layer is assumed to be T, the information is recordable onthe recording mark with a length of 2T, 3T, or more, multi-pulses areused to record the recording mark with the length of 3T or more, themulti-pulses includes a last pulse at an end thereof, and the recordingmark with the length of 3T or more is recorded provided that a width ofthe last pulse falls within a range from 0T to 1.10, the methodcomprising: the information is reproduced from at least one of therecording layers using the light.
 4. A disc drive for reproducinginformation from an optical recording medium comprising a plurality ofrecording layers on which the information is at least partly recordedusing light with a predetermined wavelength, wherein a period of channelclocks used to record at least one recording mark on the recording layeris assumed to be T, the information is recordable on the recording markwith a length of 2T, 3T, or more, multi-pulses are used to record therecording mark with the length of 3T or more, the multi-pulses includesa last pulse at an end thereof, and the recording mark with the lengthof 3T or more is recorded provided that a width of the last pulse fallswithin a range from 0T to 1.10, the disc drive comprising: a lightemitter configured to emit light to any of the recording layers, a lightreceiver configured to receive light reflected from the recording layerto which the light is emitted, and a reproducer configured to reproducethe information recorded on the medium, based on the reflected light.